Federal and state officials are planning a multimillion-dollar cleanup of contaminated ground water at the Sacramento Army Depot, to begin next year. Base spokesman Mark DeFrances said the 300-page cleanup plan seeks to eliminate high concentrations of toxic chemicals found in base ground water since 1981. Tests of wells at the base in February, 1986, found high levels of tricholoethylene, the solvent commonly known as TCE, which was dumped at the depot several decades ago by workers cleaning and overhauling Jeep and truck engines. Currently, the depot mostly repairs electronic equipment. About $3 million already has been spent on studies and cleanup efforts, and another $3 million probably will be spent to remove the chemicals, DeFrances said, in addition to $1.5 million for monitoring test wells.